Integrated-interleaved low density parity check (LDPC) codes

[0001] The present invention relates generally to error correcting codes, and more particularly, to integrated-interleaved encoding and decoding techniques.

[0002] Error correcting codes allow data errors to he detected and corrected, provided the number of errors or the characteristics of the errors fall within the correction capabilities of the code that is used. Integrated-interleaved codes, for example, are systematic codes (i.e., the input data is included or otherwise embedded in the encoded data) that generate multiple codewords, each of which is associated with a particular level. The integrated-interleaved coding scheme can he used to compensate for format inefficiencies due to small block lengths and he deployed in distributed storage systems.

[0003] Generally, methods and apparatus are provided for integrated-interleaved Low Density Parity Check (LDPC) coding and decoding. According to one aspect of the invention, integrated-interleaved LDPC encoding is performed by obtaining at least a first data element and a second data element; systematically encoding the at least first data element using a submatrix H₀ of a sparse parity check matrix H₁ to obtain at least a first codeword; truncating the at least first data element to obtain at least a first truncated data element; systematically encoding the at least second data element and the at least first truncated data element using the sparse parity check matrix H₁ to obtain a nested codeword; and generating a second codeword based at least in part on a combination of the first codeword and the nested codeword.

[0004] A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.

[0009] Various aspects of the invention are directed to integrated-interleaved LDPC encoding and decoding techniques. A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.

[0010] Integrated-Interleaved Coding Scheme

[0011] The integrated-interleaved coding scheme nests a set of m component codewords with v (v<m) more powerful (e.g., second or higher level) codewords in the nested layer which is a subcode of the component layer. Thus, v can be considered a number of second level codewords. The nested layer enables the correction of up to v component words that fail by self-decoding. For a more detailed discussion of the integrated-interleaved coding scheme, see, for example, U.S. Pat. No. 5,946,328, entitled “Method and Means for Efficient Error Detection and Correction in Long Byte Strings Using Integrated Codewords;” M. A. Hassner et al., “Integrated Interleaving—a Novel ECC Architecture,” IEEE Trans. Magnetics, vol. 37, 773-775 (March 2001); and/or U.S. Pat. No. 8,161,360, entitled “Integrated Interleaved Codes,” each incorporated by reference herein.

[0012] Under an exemplary two-level integrated-interleaved coding scheme, let {C_i}_i=0¹ be (n, k_i, d_i) over the Galois field GF(q) such that C₁⊂C₀ and d₁>d₀, where C_i, i=0, 1, explicitly assume cyclic components codes, such as Reed-Solomon codes (possibly shortened). Denote by α a primitive element of GF(q). An integrated-interleaved code is defined as follows

[0013] $\begin{array}{cc}C\stackrel{\Delta }{=}\left\{c=\left[c_0,c_1,c_2,\dots ,c_{m-1}\right]:c_i\in C_0,\sum _{i=0}^{m-1}{\alpha }^{\mathrm{bi}}{c}_i\in C_1,b=0,1,2,\dots ,v-1\right\},& \left(1\right)\end{array}$
where v<m<q.

[0014] Integrated-Interleaved LDPC Coding Scheme

[0015] According to one aspect of the present invention, the above integrated-interleaved code description is extended to LDPC codes with respect to v=1. Let H₁ be a sparse parity check matrix of C₁(n, k₁) LDPC code and H₀ be a submatrix of H₁ corresponding to C₀(n, k₀) LDPC code. An exemplary integrated-interleaved LDPC code can be defined as follows:

[0016] $\begin{array}{cc}C\stackrel{\Delta }{=}\left\{c=\left[c_0,c_1,c_2,\dots ,c_{m-1}\right]:H_0{c}_i^T=0,{H_1\left(\sum _{i=0}^{m-1}{c}_i\right)}^T=0\right\}& \left(2\right)\end{array}$

[0017] FIG. 1 illustrates an exemplary communication system 100 in which aspects of the present invention can be employed. As shown in FIG. 1, a transmitter 110 includes an integrated-interleaved LDPC encoder 200, as discussed further below in conjunction with FIGS. 2 and 3. Data is encoded using an integrated-interleaved LDPC code and any additional processing is applied as needed or appropriate. The processed data is then transmitted over a communication network 130. The communication network 130 may be embodied, for example, as any combination of wired and/or wireless communication devices. A receiver 150 receives a signal from the network 130 and processes the signal, including decoding the signal using an integrated-interleaved LDPC decoder 400, as discussed further below in conjunction with FIG. 4. Typically, a communication network 130 is noisy and the signal received by the receiver 150 is typically corrupted by noise.

[0018] In one or more exemplary embodiments, an integrated-interleaved LDPC code is used to compensate for format inefficiencies (e.g., due to a short block length and/or to reduce hardware costs in designing codes of a relatively long block length). In further embodiments, an integrated-interleaved LDPC code is used in another application besides the exemplary example shown in FIG. 1.

[0019] Aspects of the present invention provide a particular mapping or coding associated with integrated-interleaved LDPC coding. In one or more exemplary embodiments, a second level has a single component codeword and in other embodiments the second level has two or more codewords.

[0020] FIG. 2 is a block diagram of an exemplary two-level integrated-interleaved LDPC encoder 200 incorporating aspects of the present invention, for the case where m=4 and v=1. Generally, the exemplary integrated-interleaved LDPC encoder 200 of FIG. 2 aligns input messages a₀, a₁, a₂, a₃, and then linearly combines the input messages a₀, a₁, a₂, a₃, for the nested-layer encoding. As discussed hereinafter, the first step systematically encodes the messages a₁, a₂, . . . , a_m−1, with respect to H⁰, and consequently yields component codewords c₁, c₂, . . . , c_m−1, respectively.

[0021] Thus, as shown in FIG. 2, the exemplary integrated-interleaved LDPC encoder 200 comprises systematic encoders 240-1 through 240-3 that are configured to receive and encode input data a₁, a₂, a₃, respectively, using submatrix H₀, as defined by Eq. (2). First-level codewords c₁, c₂, c₃, are generated by systematic encoders 240-1 through 240-3, respectively.

[0022] To obtain the exemplary second-level codeword c₀*, truncated input, data a₁, a₂, a₃, is added to a delayed version of input data a₀ generated using delay element 210. Denote by a′_i the truncated message of a_i, a′_i=[a_i,0, a_i,1, . . . , a_i,k1⁻¹]. The original input messages a₀, a₁, a₂, a₃ have a length k₀ and the truncated messages a′₁, a′₂, a′₃ have a length k₁ (k₀>k₁).

[0023] As shown in FIG. 2, the left-aligned summation a₀+Σ_i=1^m−1a′_i (using delay element 210 for alignment and adder 220 for summation) is selected by multiplexer 225 and systematically encoded at stage 230 with respect to H₁ to yield a nested codeword c.

[0024] As shown in FIG. 2, adder 250 is configured to receive the first-level codewords c₁, c₂, c₃, as well as the nested codeword c to perform the following operation to generate the exemplary second-level codeword c*₀:

[0025] $\begin{array}{cc}{c}_0^{*}\stackrel{\Delta }{=}\stackrel{\_}{c}-\sum _{i=1}^{m-1}{c}_i& \left(3\right)\end{array}$

[0026] In the exemplary embodiment of FIG. 2, where v is equal to 1, the second level has a single component codeword. In cases where v is greater than 1, the second level has a plurality of component codewords.

[0027] It can be verified that c*₀εC₀, and furthermore, c*₀+Σ_i=1^m−1c_i=cεC₁.

[0028] FIG. 3 is a flowchart illustrating an embodiment of an exemplary encoding process 300 for two level integrated-interleaved LDPC encoding, where m=4 and v=1. As shown in FIG. 3, the exemplary encoding process 300 initially obtains input messages a₀, a₁, a₂, a₃ during step 310. Thereafter, first level codewords c₁, c₂, c₃ are generated during step 320 by performing systematic encoding with respect to H₀.

[0029] The truncated version of input message a₀ is then delayed during step 330 using delay element 210 to align the truncated input message a₀ with input messages a₁, a₂, a₃. Adder 220 then performs a left-aligned summation a₀+Σ_i=1^m−1a′_i during step 340. The sum generated by adder 220 is then systematically encoded with respect to H₁ during step 350 to generate a nested codeword c.

[0030] Finally, adder 250 receives the first-level codewords c₁, c₂, c₃, as well as the nested codeword c during step 360 to generate the exemplary second-level codeword c*₀, as follows:

[0031] $c_0^{*}\stackrel{\Delta }{=}\stackrel{\_}{c}-\sum _{i=1}^{m-1}{c}_i.$

[0032] Integrated-Interleaved LDPC Decoding Scheme

[0033] FIG. 4 is a flowchart illustrating an embodiment of an exemplary decoding process 400 for two level integrated-interleaved LDPC decoding, where m=4 and v=1. As shown in FIG. 4, the exemplary decoding process 400 initially receives a channel word y=[y₀, y₁, . . . , y_m−1] during step 410. The exemplary decoding process 400 applies a min-sum decoding to each component word y_i, i=0, 1, . . . , m−1 during step 420. If it is determined during step 430 that each component word is decoded successfully, then the corrected codeword is returned during step 440. If it is determined during step 430 that two or more component words incur decoding failure, then a decoding failure is declared during step 450. If it is determined during step 430 that one component word incurs a decoding failure, say, y_j, then all other passing decoded codewords are added to the failed codeword during step 460, such that y=y_j+Σ_i≠jc_i and then y is decoded with respect to H₁ during step 470. If successfully decoding to a codeword c, then declare c_i=c−Σ_i≠jc_i during step 480.

[0034] While aspects of the present invention have been illustrated using integrated-interleaved LDPC encoding and decoding for v equal to 1, the present invention can be extended to additional values of v, as would be apparent to a person of ordinary skill in the art. In addition, while aspects of the present invention have been illustrated using two-level integrated-interleaved LDPC encoding and decoding, the present invention can be extended to higher-level integrated-interleaved LDPC encoding and decoding, as would be apparent to a person of ordinary skill in the art.

[0035] Process, System and Article of Manufacture Details

[0036] While a number of flow charts herein describe an exemplary sequence of steps, it is also an embodiment of the present invention that the sequence may be varied. Various permutations of the algorithm are contemplated as alternate embodiments of the invention. While exemplary embodiments of the present invention have been described with respect to processing steps in a software program, as would be apparent to one skilled in the art, various functions may be implemented in the digital domain as processing steps in a software program, in hardware by circuit elements or state machines, or in combination of both software and hardware. Such software may be employed in, for example, a digital signal processor, application specific integrated circuit, micro-controller, or general-purpose computer. Such hardware and software may be embodied within circuits implemented within an integrated circuit.

[0037] Thus, the functions of the present invention can be embodied in the form of methods and apparatuses for practicing those methods. One or more aspects of the present invention can be embodied in the form of program code, for example, whether stored in a storage medium, loaded into and/or executed by a machine, or transmitted over some transmission medium, wherein, when the program code is loaded into and executed by a machine, such as a computer, the machine becomes an apparatus for practicing the invention. When implemented on a general-purpose processor, the program code segments combine with the processor to provide a device that operates analogously to specific logic circuits. The invention can also be implemented in one or more of an integrated circuit, a digital signal processor, a microprocessor, and a micro-controller.

[0038] As is known in the art, the methods and apparatus discussed herein may be distributed as an article of manufacture that itself comprises a computer readable medium having computer readable code means embodied thereon. The computer readable program code means is operable, in conjunction with a computer system, to carry out all or some of the steps to perform the methods or create the apparatuses discussed herein. The computer readable medium. may be a tangible recordable medium (e.g., floppy disks, hard drives, compact disks, memory cards, semiconductor devices, chips, application specific integrated circuits (ASICs)) or may be a transmission medium (e.g., a network comprising fiber-optics, the world-wide web, cables, or a wireless channel using time-division multiple access, code-division multiple access, or other radio-frequency channel). Any medium known or developed that can store information suitable for use with a computer system may be used. The computer-readable code means is any mechanism for allowing a computer to read instructions and data, such as magnetic variations on a magnetic media or height variations on the surface of a compact disk.

[0039] The computer systems and servers described herein may each contain a memory that will configure associated processors to implement the methods, steps, and functions disclosed herein. The memories could be distributed or local and the processors could be distributed or singular. The memories could be implemented as an electrical, magnetic or optical memory, or any combination of these or other types of storage devices. Moreover, the term “memory” should be construed broadly enough to encompass any information able to be read from or written to an address in the addressable space accessed by an associated processor. With this definition, information on a network is still within a memory because the associated processor can retrieve the information from the network.

[0040] It is to be understood that the embodiments and variations shown and described herein are merely illustrative of the principles of this invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention.